User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.16; rv:84.0) Gecko/20100101 Firefox/84.0

Steps to reproduce:

On macOS, when I press Cmd+Q multiple times, I get multiple "Quit and close tabs?" dialogs

Actual results:

Must cancel multiple dialogs. See attached .mp4.
macOS 11.1, Firefox 84.0.1

Expected results:

Only one dialog should be displayed no matter how many times Cmd+Q is pressed

I confirm this issue as valid on Mac OS 11.0.1 and 11.1 with Firefox ESR v78.6.0esr through Nightly v86.0a1.
This issue does not occur on Windows 10 systems.
I would have preferred to find a possible regression range using mozregression, but it appears that it does not work. Logging bug now.

Will be back with information regarding a possible regression range.

This issue occurs as far back as Firefox Release v60.0 so I will assume that this is no recent regression.